The desirability of removing mercury from gaseous streams that might introduce the mercury into the atmosphere, such as from flue gases emitted in combustion operations, is increasingly well known.
Some attempts to remove mercury from flue gas employ solid adsorbents that are introduced into the flue gas stream. The mercury is removed from the flue gas atmosphere onto the adsorbent, and the mercury-bearing adsorbent is separated from the flue gas by the equipment which also separates other solid materials such as fly ash from the flue gas before the flue gas is emitted into the atmosphere.
Fly ash recovered from the flue gas of industrial combustion operations such as coal-fired electric power plants is often useful as a component of cement. It is desirable to be able to use fly ash in this way even when the fly ash contains solid adsorbents that were used as described above to remove mercury from the flue gas.
When a cement composition is combined with water and other components to create a mixture that can be poured or otherwise formed into what will become a solid product when the cement solidifies, a surfactant or other air-entraining additive is often added to the cement in order to permit bubbles to form within the cement mixture. The bubbles become voids within the solidified product so that any water that permeates into the solid product may expand into the voids if it freezes, so as not to jeopardize the integrity of the solid product itself.
However, it is well known that the presence with the fly ash of PAC (powder activated carbon) adsorbents used for mercury removal from flue gas can interfere with the ability to form the desired bubbles in the cement composition by air-entraining additive(s). Thus, there is a need to find solid adsorbents for mercury removal, and methods for making them, that overcome this interference.